1. Field of the Utilization
The present invention relates to an antenna for communication systems such as automobile telephones, portable telephones, etc. which is ideal as an antenna installed both indoors and outdoors.
2. Prior Art
When these types of antennas are installed on indoor ceilings, etc., they are eyesores if they are large, and it would be difficult to secure a location for installing such large antennas. Accordingly, antennas that are compact and light in weight which can be manufactured at a low cost are desired.
FIG. 5 shows one example of a conventional antenna of this type. The antenna shown in FIG. 5 is comprised of: a rod-form first antenna element 1 which has an electrical length of lambda/4 (where lambda is the wavelength of the electromagnetic waves in the frequency band used); a cylindrical second antenna element 2 which has an electrical length of lambda/4 and is installed at the base end of the first antenna element 1; and a coaxial line 3 with a tip end thereof inserted into the hollow interior of the second antenna element 2 so as to electrically connect the second antenna element 2 and the first antenna element 1.
The conventional antenna described above is a type of so-called "sleeve antenna" and has an electrical length of lambda/2. Accordingly, the total length of the antenna is great; and therefore, the antenna takes up considerable space. Accordingly, when an antenna is installed indoors, the antenna is a severe eyesore. In addition, it is difficult to secure a location where the antenna is installed. Furthermore, there are also problems with directivity.